Fluoroplastic coatings as protection against corrosion for containers and pipes were developed only about fifteen years ago. They have excellent chemical and physical properties. The strong fluorine-carbon bond and the almost complete shielding of the carbon chains by the fluorine atoms result in universal chemical resistance of the fluoroplastics. The latter are also characterized by temperature stability in the range of about 150.degree. C. to 300.degree. C.
However, the coatings consisting of these materials show different behavior. Due to their thermoplastic nature these fluoroplastics have a certain degree of permeability for gas or vapor molecules at higher temperatures. This permeability depends on the thickness of the layer and on the given temperature. An increase in layer thickness reduces diffusion; an increase in temperature increases it. For these reasons, long-lasting protection against corrosion could not be realized up to now by coatings with fluoroplastics.
It has been proposed to incorporate a barrier in the coatings. The tests were based on the idea of incorporating pigments and fillers to prolong the path of the diffusing material to the metal surface. The protective effect can be improved if the additives have a barrier effect due to their specific particle shape (for example tabular pigment particles) and appropriate orientation in the layer. However, such additives are not suitable for plastic coatings since they are not chemically resistant. Furthermore, the diffusion path is only prolonged; this does not solve the problem of preventing diffusion. The production of greater layer thicknesses was not possible up to now for technical reasons. Using the conventional methods of protecting containers or pipes against corrosion by coating them with fluoroplastics, layer thicknesses of only about 0.5 mm have been obtained, which are too small for sufficient protection against corrosion.
The present invention is therefore based on the problem of producing long-lasting protection against corrosion for containers or pipes by coating them with fluoroplastics.